Biofouling is the settlement and subsequent growth of marine organisms on submerged surfaces. Because these surfaces are in many instances artificial, e.g. boat hulls, oil and gas platforms, aquaculture nets and enclosures, fouling organisms present a significant problem to human activities in the ocean. The formation of fouling communities on boats increases drag; reducing ship speed while increasing fuel costs and dry dock time; fouling of semi-permanent offshore structures increases structural loading and corrosion, and fouling of nets and enclosures adds significant costs to the maintenance of aquaculture systems. The increased fuel usage, drydocking, structural inspection, maintenance etc. resulting from biofouling has been estimated to cost the world's marine industries over $3.5 billion dollars per year.
Fouling is primarily combatted by the use of antifouling coatings which are applied to the surfaces of boats or other marine structures. These coatings rely almost exclusively on heavy metals particularly copper and tin based compounds for their active ingredients. These compounds leach into the water from the coating, killing fouling organisms. Unfortunately, these compounds also kill non-target organisms in the environment at large, and the general environmental effects of these compounds is of worldwide concern. (Dalley 1989). Tin based coatings are particularly toxic, and such coatings are now partially (restricted to vessels &gt;25 m in length in NSW, Europe and parts of the USA) or totally (Japan) banned in the world's waterways. It is generally accepted that the use of tin (specifically tributyl tin) based coatings will be completely banned in most countries within the next 5-10 years.
The demise of heavy-metal based antifouling coatings has prompted the search for more environmentally benign antifoulants, and one of the most promising alternative technologies is the use of naturally occurring antifouling compounds derived from natural metabolites from marine organisms (Holmstrom and Kjelleberg 1994).
Marine organisms such as seaweeds, sponges, etc. are also submerged surfaces, and they must detre fouling of their bodies to avoid increases in drag (and being pulled off the bottom) or being smothered. It is now abundantly clear that one of the ways in which marine organisms defend against fouling is via the production of natural antifoulants. Because these compounds already occur in nature, it is thought that these natural metabolites will be less environmentally damaging that the current heavy-metal based paints. A number of metabolites or extracts from marine organisms with antifouling activities typically tested against barnacle larvae have now been identified (Holmstrom and Kjelleberg 1994, Targett et al. 1983, Standing et al. 1984, Rittschof et al., 1985, Gerhardt et al. 1988, Keifer et al. 1986, Sr Mary et al. 1993, Maki et al. 1989, Holmstrom et al. 1992, Todd et al. 1993).